Thermoelectric generator and casing therefor



July 29, 1952 c. E. BoDEY 2,505,296

` THERMoELEcTRrc GENERATOR AND cAsING THEREFOR Filed Nov. 24, 1947 Snoentor Eli/72H55 OEY @7e/YM Gttorneg Patented July 29, 1952 THERMOELECTRIC GENERATOR AND CASING THEREFOR Charles E. Bodey, St. Paul, Minn.,v 'assignor to Minneapolis-Honeywell RegulatorCompany, Minneapolis, Minn., a corporation of Delaware ApplicationNovember 24, 1947, serial Nojrsmeesl 1 ThisV -invention relates to improvements in thermoelectric generators o`f the type comprising a thermocouple unit and an associated burner for heating said unit. More particularly,` the invention is Vconcernedwith'the unit which transforms heat Vinto Velectrical energy, namely, the thermocouple unit of the generator.

Thermoelectric `generators of the above mentioned type are well known in the art. The nu- Vmerous designs differ widely as to the burner construction Vand the construction of the associated thermocouple or combination of lthermocouples, commonly known as thermopiles, and as Yto their relative positions.

v While Ymost of the prior art generators of the above mentioned type are satisfactory for Va good Vmany of .the applications for which they are `designednone of them is wholly satisfactory for use in `an installation requiring that the .thermoelectric generator be small .in size, must operate with relatively small heat generation, and must produce a comparatively high .and Vuniform elec-l trical output throughout Aits operating life. This deficiency on the part of the prior art devices is -due to the .fact that the cases on the thermocouples gradually Yoxidize inside and out and,

particularly, at the hot junction ends thereof when said ends Vare continuously heated. rihe oxide, being a poor heat conductor, causes a decrease in electrical output andthus faulty operation of the system controlled by said electrical output. This makes it necessary for the systems in which the prior art devices are used to be checked and adjusted from time to time to -keep the systems in proper working order.

. An `object of this invention is to provide a small and relatively inexpensive thermopile type of an i-.elec-tric -generator that substantially maintains its electrical output throughout its operating life. .Another object of the invention is to provide Va thermopile that is highly efficient.

Y A furtherobject of the invention is to provide a thermopile case or shell which may be A:formed substantially from sheet material.

Another object of the invention is to provide `a Vthermopile case or shell that has dark oxil away from an associated burner for heating it.

Y v.Still further objects of the invention will become apparent upon reading the following detaileddescription of the invention in conjunction w'iththe accompanying drawings wherein:

v'6 Claims. (Cl. 13G-744)' 2 VFigure 1 "is an elevational view of the thermoelectric generator with parts thereof broken away;

Figure 2 is a cross-sectional View taken on a plane extending longitudinally `throughthe therymopile;

Figure v3 is a cross-sectional View taken on Athe line'S-B of Figure 2;

Figure 4 is a bottom view of the thermopile with portions .thereof broken away; and

Figure' isa plan View of the main body portion of Vthe thermopile case Aas it appears before being bent into the shape of an open-sided casing.

Referring now to Figure 1 'of the drawing, the therrnoelectric generator comprises a thermopile, generally designated by the numeral I0, a pilot burner '.I I, and a bolt I2 passing through bracket members i3 and I4 on the thermopile and 'pilot burner, respectively, for adjustably securingthem together.

The details of the pilot burner `I I form no part of this invention. It is of the Well known type wherein orifices are provided for directing one ame against the upper hot junction end of the thermople and another `flame over an associated mainburner (not shown) to ignite it. A runner or carrierflame, for reigniting either 'one of .said orifices from the other orifice, yis provided for by means of a slot in `the side wall 'of the pilot burner extending from 'one orice to the other.

The bracket I4, which is staked or otherwise securely fastened around the'pilot burner body, is adapted to be secured to the wall Vof a furnace (not shown) or a main burner (not shown) by any suitable fastening means. The right hand end of the bracket I4 is slotted so as to receive the ythermopile I0 and has spaced upper and lower walls I5 and I6, respectively, which are adapted to snugly receive therebetween a laterally projecting portion I1 of the bracket I3. mentioned bolt 'I2 passes freely through .an opening in the bottom wall I6 of the bracket I4, through spaced slots in the laterally projecting portion I1-of the' bracket I3 and is screw-threaded into an opening in the top wall I5. Tightening of the 'bolt I2 draws the bottom wall I6 and upper wall I5 tightly against the portion I1 to frictionally hold the thermopile IIJ in its adjusted position relative to the pilot burner II.

Referring now to Figures 2, 3, 4 and 5, the thermopile l0, which forms the ,major portion of thisinvention, comprises a casing I8 which is The above cut into the shape shown in Figure 5, then stamped to form the indentations I9, then bent sharply along the dotted lines to form unjoined side walls and 2 I, having ears 20a and 2 Ia, and bottom Wall 22. The top wall 23 is also bent but on a Vsuiciently large radius so as to cause its side edges to bear against the inner surfaces of walls 20 and 2| adjacent their upper edges. The bracket I3 is then spot-Welded or connected in any other suitable manner to the front Wall 24 of casing I8.

A cover 25, similarly formed from the same kind of sheet material, has an extruded `portionV Cover 25 also has a bottom ange 29, side flanges and 3| and projection 32 which bear against the outer surfaces of the Walls 2'2, 20, 2I and 23, respectively, and hold said walls in their folded positions. Slots 25a. in the cover receive the ears 20a and 2Ia which are bent over on the outer surface of the cover to hold it on the casing I8.

The above mentioned casing and cover have darkened or blackened inner and outer surfaces, as illustrated at 33 and 34, respectively, which are so made by dipping the casing and cover in a very hot bath of sodium dichromate for from five to ten minutes. This treatment oxidizes the surface iron, chromium, and nickel in the sheet material to form substantially black inner and outer surfaces thereon. This blackening or oxidizing of the surfaces of the casing and its cover enables the complete case to perform many useful and improved functions to be described hereinafter.

A simple thermopile comprising series-connected, alternately-spaced, thermoelectrically dissimilar metals 35 and 36 having oxidized insulation surfaces, as illustrated at 36a, is of the same general shape as the above mentioned casing, but has smaller overall dimensions. The hot and cold junctions are preferably made by spot-welding. The end elements 35and 36 have downwardly and inwardly extending projections 3l and 3S, respectively, thereon which are wrapped around and soldered or otherwise suitably secured to the ends of lead wires 39 and 40, respectively. These projections and ends of the lead wires are held spaced'apart by means of an insulation plate 4I. The thermopile elements 35 and 36 are held spaced from the casing I8 and cover 25 by means of strips of mica or other insulating material 42 and 43 and indentations I3 as well asrby heat conducting, electrically insulating, ceramic cement 44 packed into and lling the case. Y

In assembling the above mentioned v,elements of the thermopile, the casing I8 is held with its longitudinal axis in a horizontal position, with the open side up. A thin layer of the ceramic cement 44 is spread over the innerl surface of the wall 24. rI'he sheet of mica 42. is then positioned over this cement to insure spacing of the longitudinal edges of the thermopile velements from said wall 24. This sheet of. mica extends from the wall 22 to approximately three-fourths of the length of the wall 24. The thermopile elements are then inserted so asto rest on this sheet of mica. then positioned over the opposite edges of the thermopile elements and is `of such length Yas to extend substantially the full length of said edges. More of the same ceramic cement is then forced all around the thermopile elementswith rlhe second sheet of mica 43 is.

a surplus amount piled up thereon so as to force some of the cement up into the extruded portion 26 of the cover member 25 in the next step. This next step consists in sliding the cover 25 down over the cable 28 into its position on the open side of the casing with the ears 20a and 2 Ia. extending through the slots 25a. The ears 20a and 2Ia. are then bent inwardly over the outer surface of the cover 25 to lock it in position. The final processing step consists of baking the assembled unit to harden the cement.

Operation With the thermopile mounted on the pilot burner as shown in Figure 1, with the pilot burner connected to a suitable source of fuel and the leads 39 and 40 of the thermopile connected to a suitable load such as the above mentioned system, a flame issuing from one of the orifices in the pilot burner and impinging on the upper portion of the thermopile causes the generation of electricity by the thermopile and energization of the load. Depending upon the nature of the fuel being burned, whether it is natural gas, or manufactured gas or mixtures of both, the flame will have certain characteristics. It has been found that due to these differing characteristics, it is highly desirable, if not absolutely necessary, to be able to adjust the position of the thermopile with respect to the pilot burner so as to have the flame impinge properly on the thermopile. It can be readily seen that the mounting bracket for applicants thermopile permits easy and quick adjustment thereof to assure optimum efficiency of operation of the generator by merely loosening screw I2, sliding the thermopile to the proper position, and then tightening the screw.

Furthermore, the blackening on the outer surface of the hot junction end of the thermopile increases the radiant heat absorption properties thereof which partly offsets the loss in efficiency or output due to reduction of heat transfer by conduction thru the oxidized or blackened surfaces of the case to the ceramic materialand the hot junction ends of the thermopile elements.

Likewise, the blackened outer surface at the cold junction end of the thermopile casing, due to its better heat radiating properties, more than oifsets the loss of eiiiciency due to the drop in heat transfer by conduction from the cold junction end of the thermopile element through the blackened inner and outer surfaces of the cold junction end of the shell or case.

It is thus seen that the provision of highly oxidized inner and outer wall surfaces of the thermopile shell performs multiple functions when applied to a thermoelectric generator of the type. described. First, due to the fact that the inner and outer surfaces are highly oxidized in the manufacture of the device, there will be no change in the condition of the surfaces throughout the thermopiles operating life. Secondly, the blackened outer surface provides more efficient radiant heat absorption from the flame and emission of heat fromthe -cold junction end of the case, enabling a smaller quantity of gas to be burned or the use of a thermopile of small size. Thirdly, the blackened outer surface at the cold junction end of the thermopile provides more efficient heat dissipation than an unblackened surface so as to maintain the cold junction end at a lower temperature and thus produce a higher output from the thermopile. This is due to the fact that a greater percentage of the heat dissipated there is due to radiation.

Fourthly, the above mentioned blackened surfaces enables the thermopile to be of small size for use in cramped spaces, due to the fact that more stable heating and better cooling of the hot and cold junctions, lrespectively, is obtained without having to use prior art cooling ns on the case.

It is also to be noted that by having the hot junction ends of the thermopile elements welded together near their ends and the side edges thereof adjacent the front sur-face 24 of the casing, and all of the edges of said elements facing said front wall, the burner flame is spread over this flat surface front wall so as to uniformly heat these edges very close to the hot junctions.

As modifications of this invention may be made Without departing from the spirit thereof, it is to be understood that the scope of the invention is to be determined solely by the appended claims.

I claim as my invention:

1. In a thermoelectric generator, a thermoelectric unit, a protective case for said thermoelectric unit comprising a main body portion of oxidized sheet material in the form of an opensided casing, ears on said casing extending beyond said open side, and a cover member having openings therein through which said ears extend and flanges thereon engaging side walls of said body portion, said ears being bent transversely for holding the containers side walls together and said cover member' on said container.

2. In a thermoelectric generator, a thermoelectric unit, a steel case having oxidized inner and outer surfaces for enclosing said thermoelectric unit, and heat-conducting electricity insulating material between said unit and said case.

3. In a thermoelectric generator, a thermoelectric unit formed of dissimilar metal elements, the surfaces of which are oxidized, a protective case for said thermoelectric unit, said case being composed at least partly of steel and the inner and outer surfaces thereof being highly oxidized.

4. A thermoelectric generator comprising a metallic case having one end thereof so con- 6 structed as to operatively withstand the impingment of a flame thereon, said end having oxidized inner and outer surfaces at the point of flame impingement, and a thermocouple Within said case having a hot junction portion positioned within said end of said case.

5. In a thermoelectric generator, a thermoelectric unit having a hot junction and a cold junction, a thin wall metallic case housing at least said hot junction and arranged to be heated by a llame adjacent said hot junction, said case having highly pre-oxidized inner and outer surfaces.

6. In a thermoelectric generator, a thin wall metallic protective case for a thermoelectric unit wherein the inner and outer surfaces at least at the area of the case to be heated are highly oxidized.

CHARLES E. BODEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,017,084 Wilson Oct. 15, 1935 2,126,656 Pack Aug. 9, 1938 2,149,448 Lederer et al. Mar. 7, 1939 2,181,843 Wantz Nov. 28, 1939 2,186,948 Alder Jan. 16, 1940 2,267,742 Mantz Dec. 30, 1941 FOREIGN PATENTS Number Country Date 190,657 'Great Britain Dec. 28, 1922 OTHER REFERENCES Lewis et al.. J., Applied Physics, vol. 11 (1940), pp. 703-4.

Rohsenow et al., Trans'. A. `S. M. E., vol. 69, Aug. 1947, p. 702. I

King, W. J., Mechanical Eng., vol. 54 (1932), p. 494. 

